As it is known, metallurgic furnaces and, in particular, electric arc-furnaces for the production of steel of the older generation comprise a metal vat, in turn comprising a basin or crucible, a shell and a dome, coated inside with refractory material which, due to thermal, mechanical and chemical stress suffered during the operation cycles of the furnace, can suffer from erosion and damage.
In more modern metallurgic furnaces, the walls that define the shell and that project above the basin or crucible for containment of the metal to be treated and possibly the upper closure dome are made with metal panels that are cooled with water.
During the operation of the furnace, operation that, as known, is typically intermittent or discontinuous, such panels cyclically undergo mechanical, thermal and chemical stress, which, over time, damage their structural integrity, leading, for example, to the formation of cracks and fissures.
In particular, during the step of loading the metal to be treated, typically in the form of a scrap metal, the panels and, in particular, the face thereof facing the interior of the furnace is subjected to loads and mechanical actions. During the melting, formation and treatment steps of the metal bath, on the other hand, the panels are exposed to the high temperatures that are reached inside the furnace.
As already mentioned, the strength and the cyclicity of the mechanical, thermal and also chemical stress, damage the structural integrity of the panels and substantially reduce the average life span, making it necessary for there to be frequent maintenance or replacement operations.
The formation of fissures and cracks, moreover, causes there to be leakages of water that, if occur inside the furnace, can generate operation conditions that are extremely dangerous and that can lead to explosions.
Indeed, if the water that has come out from the panels is enclosed in the liquid metal bath or infiltrates into the refractory coating, the immediate evaporation, with an increase of the volume thereof, generates a sudden and rapid expansion and explosion. Events of this kind cause further damage of the furnace itself and jeopardise the safety of the work environment.
At the end of each operation cycle of the furnace, the integrity of the cooling panels is visually inspected by the workers.
During the operation of the furnace, on the other hand, possible leakages of water are detected and indicated through detection and signalling systems that are associated to the furnace.
It is known for there to be, for example, systems for detecting and signalling water leakages based upon the chemical analysis of the exhaust gases of the furnace of which they monitor the steam and hydrogen content.
Systems based upon the detection of the flow-rate, pressure and temperature of the water circulating in the panels are also known, like those for example described in US2009/0148800.
In the case in which the inspection of the panels carried out between two subsequent operation cycles of the furnace highlight the presence of a damaged panel or a water leakage is indicated during the operation of the furnace, it is necessary to provide for replacing and repairing it. Such maintenance interventions require the furnace to be stopped for a long time and, thus, a non-planned halt of the production, with consequent economic losses.
It is also possible for a water leakage to be indicated during critical operation steps of the furnace such as, for example, the tapping step. In such a case it is not possible to stop the furnace so as to intervene on the damaged panel before such an operation step has been completed. In such a situation, the flow of water which supplies the discussed panel is obstructed; this causes there to be further damage of the panel itself which, often, can no longer be repaired and restored.
From what has been described above it is clear that the panels, cooled with water, of the known type require frequent replacement and maintenance interventions, even not planned, which have a significant impact upon the productivity of a furnace, which must be stopped and kept off for the time necessary for carrying out such interventions.
The average life of the panels themselves, moreover, is limited and the relative maintenance and repairing interventions are expensive.
It is moreover obvious that the panels cooled with water of the known type can lead to dangerous operation conditions both for the integrity of the furnace itself, and for the workers.